Integrated circuits include a metallization in the form of a pattern of a conductive material, such as a metal or conductive polycrystalline silicon, extending over and insulated from the surface of the semiconductor substrate of the integrated circuit. The metallization extends through openings in the insulation between the metallization and the substrate surface and makes ohmic contact with the substrate to electrically connect the various components of the integrated circuit. As the number of components in integrated circuits has increased, it was found that a single level of the metallization could not connect all of the components. Therefore, it became necessary to use multiple levels of metallization with a layer of insulating material between adjacent levels.
A problem that has been found in making multi-level metallization arises from the fact that the conductive layer forming the first level has a thickness which causes it to project above the surface of the insulating layer on which it is formed. When the interlevel insulating layer is coated over the first level, it forms a hump or projection which extends over a portion of the first level. When applying the second level of the metallization, problems arise in obtaining complete and unbroken coverage of the second level over the humps formed by the first level, particularly where the humps have steep, sharp sides. One method of overcoming this problem is to form the humps with sides which are not steep, i.e., have a small angle with respect to the planar surface so that the surface over which the second level extends is smoother. However, a better method of overcoming this problem is to planarize the first level by depositing a layer of an insulating material to fill the space between the first level metal deposits and thus form a surface planar with the surface of the first level metallization. This completely eliminates any humps in the inter-level insulating layer and the second level of the metallization is formed over a planar surface.